Apparatus and method for conveying amplified sound to ear

ABSTRACT

An earmold and a method of manufacturing an earmold for a hearing aid that conveys amplified sound from the hearing aid into the ear canal to a closed cavity adjacent the tympanic membrane. The earmold includes an acoustic conduction tube having an external diameter smaller than the ear canal and a flexible flanged tip that exerts negligible pressure on the wall of the canal. One end of the tube is held in place in the canal by the flanged tip. The opposite end of the tube may be positioned in the ear aperture by a fitting in the ear concha that may be integral with the tube. The hearing aid and the earmold leave the canal open preferably to a point past the canal isthmus.

This is a continuation-in-part of U.S. patent application Ser. No.244,398, filed Sep. 15, 1988.

BACKGROUND OF THE INVENTION

The present invention relates to hearing aids and, more particularly, toearmolds that convey amplified sound from the hearing aid to the ear.

Audiologists have long sought to provide an earmold for a hearing aidthat prevents the amplified sound from feeding back and interfering withthe operation of the hearing aid and, simultaneously, to provide anearmold that is comfortable to wear. The hearing aid art is replete withdevices that are able to meet one, but not both, of these objectives.

Feedback is the distortion of amplified sound caused by conduction ofthe amplified sound back to the microphone that receives the unamplifiedsound. Conduction occurs through the air pathway between the microphoneand receiver in the hearing aid (acoustic feedback), and through thecontact between the receiver and the surrounding housing (mechanicalfeedback). For hearing aid users with a profound hearing loss at severalor all frequencies, the acoustic feedback problem is exacerbated by theneed to generate abnormally loud sounds in the ear canal. For users witha partial hearing loss (for example, loss of hearing at highfrequencies), resolution of the acoustic feedback problem is complicatedby the need to amplify sound at some frequencies and to leave otherfrequencies unamplified.

The parts of the ear's anatomy pertinent to this invention are shown inFIG. 1. The ear canal 10 extends from the ear aperture 20 to thetympanic membrane 30. While canal size and shape may vary from person toperson, it is generally about 24 millimeters long and has an S-shape. Incross section it is an oval with the major axis in the verticaldirection near the aperture 20 and in the horizontal direction near thetympanic membrane 30. The cross-sectional area of the canal decreases atthe isthmus 40 approximately 18 millimeters from the aperture. The canalis formed from cartilage 12 and bone 16 and is lined with skin. Thecartilaginous portion is nearest the aperture 20 and is about 8millimeters long. The osseous portion, formed from the temporal bone 16,is about 16 millimeters long. The temporal bone 16 also contains thecavities of the middle and inner ear. The region outside the ear canaladjacent the aperture 20 forms a bowl known as the concha 50.

Both the ear's anatomy and an incomplete understanding of the hearingprocess contribute to the failure to produce a hearing aid for bothprofound and partial hearing loss that comfortably reduced acousticfeedback. It is known, however, that the bones in the skull play animportant role in hearing. The ear receives sound waves through themechanisms of air conduction and bone conduction. Sound waves in the airmove through an air conduction pathway (the ear canal) to the tympanicmembrane, where they are conveyed to the inner ear. Sound waves also arereceived by the temporal bone of the skull and conveyed directly to theinner ear. In the inner ear sounds from both sources are joined toproduce the full frequency spectrum of hearing. It is believed that theprocess of hearing may also include the reception of the pressure ofacoustic waves on various neural receptors in the body which are relayedto the brain for interpretation along with the inner ear's signals.

Even if the body's methods for receiving and interpreting the varioussensory signals which produce hearing were completely understood, andthey are not, the hearing process is further complicated by the factthat the major signal source, the inner ear, receives acoustic signalswhich are complex waveforms dependent upon the size, shape, porosity, etcetera of the ear canal and its surrounding tissue. Sounds receivedwithin the ear canal are reflected, refracted and, in part absorbed bythe ear canal and its surrounding structure. The sound which arrives atthe ear drum has been altered by the various wave reflections andrefractions within the ear canal and the head. Thus, the normal open-earhearing process includes complex and little understood phaserelationships among sounds arriving from the air and bone conductionpaths. The loss or distortion of one of these paths by artificialdevices can disrupt the normal phase relationships of the arrivingsignals.

One approach to reducing acoustic feedback in hearing aids has focusedon blocking the air-conduction pathway. An acoustic barrier is placed inthe ear between the receiver of the hearing aid and the outlet for theamplified sound. In one approach, the barrier is held in place byexerting pressure against the osseous and cartilaginous portions of theear canal. See, for example, U.S. Pat. No. 4,006,796 to Coehorst datedFeb. 8, 1977, and U.S. Pat. No. 4,520,236 to Gauthier dated May 28,1985. This pressure can be uncomfortable to the wearer and often resultsin the receding of the osseous and cartilaginous portions of the canalaway from the pressure, i.e., the canal becomes greater in diameter.Because the barrier conducts amplified sound to the temporal bone, thenormal phase relationships among sounds arriving from the air and boneconduction paths can be disrupted.

Other approaches have eliminated the pressure on the wall of the osseousportion of the canal and sealed the ear canal at the aperture or in thecartilaginous portions of the canal to obtain the desired reduction infeedback along the canal. See, for example, U.S. Pat. No. 3,061,689 toMcCarrell, et al., dated Oct. 30, 1962, U.S. Pat. No. 3,312,789 toLewis, et al., dated Apr. 4, 1967, and U.S. Pat. No. 2,939,923 toHenderson dated Jun. 7, 1960. These devices, however, do not deal withother problems caused by sealing the ear canal. These problems,insertion loss and occlusion effect, cause the hearing aid to producesounds which are both unnatural and uncomfortable for the wearer.

Insertion loss is the removal of a portion of sound from the ear canal.Occlusion effect is the increased transmission of sound by boneconduction when air conduction is impeded. For example, one's own voicesounds different when one talks with his ears blocked. (See also, pp.204-206 of "Bone Conduction" by Juergen Tonndorf in Foundations ofModern Auditory Theory, edited by Jerry V. Tobias, Vol. 2, pg. 197,Academic Press, New York.)

For those hearing aid users with partial hearing, the means to seal theear canal in the devices in the above-cited patents indiscriminatelydisrupt the phase relationships for all frequencies, even those to whichthe otherwise malfunctioning ear may be responsive.

The present invention recognizes that the complex phase relationships ofair and bone conduction are not completely understood. It creates anearly natural hearing environment by reducing the interference withthese complex relationships. Rather than blocking the ear canal with amassive seal, it opens the canal; rather than exerting pressure on thewall of the canal, it reduces wall contact. It reduces both feedback andinsertion loss, and all but eliminates occlusion effect.

The present invention creates a critically tuned resonant cavity in theear canal next to the tympanic membrane. The cavity is bounded by thewall of the canal, by the tympanic membrane, and by a flexible sealpositioned in the canal, preferably between the isthmus and the tympanicmembrane. The unimpeded sound received at the ear aperture movesrelatively unimpeded through the canal until it reaches the face of theflexible seal nearest the aperture. Amplified sound from the hearing aidis conveyed through the ear canal inside the conduction tube and isreleased from the tube inside the resonant cavity. The flexible seal(whose primary function is to reduce acoustic feedback through the airconduction pathway) retains many of the natural phase relationships by(1) leaving much of the canal exposed to unamplified sound, and (2)vibrating at the frequencies of the unamplified sound. Because much ofthe canal is exposed, hearing aid users with normal hearing atparticular frequencies are able to hear nearly natural sounds at thosefrequencies. Amplified sounds at the frequencies at which hearing isimpaired are enhanced by the action of the resonant cavity. The resonantcavity restores much of the natural fullness of the sound by being inharmony with the frequencies of the unamplified sound.

It is accordingly an object of the present invention to provide a novelearmold for a hearing aid which obviates may of the problems of theprior art and which retains a substantial part of the natural hearingprocess.

It is another object of the present invention to reduce hearing aidfeedback by exposing much of the ear canal to unamplified sound.

It is yet another object of the present invention to increase hearingaid user comfort by reducing the pressure on the wall of the ear canal.

It is a further object of the present invention to improve hearing aidperformance and comfort by retaining many of the natural phaserelationships among the sound pathways.

It is still a further object of the present invention to create aresonant cavity next to the tympanic membrane for retaining many of thenatural phase relationships of the amplified frequencies.

It is yet a further object of the present invention to provide a methodfor making an earmold for a hearing aid that reduces feedback and iscomfortable to wear.

These and many other objects and advantages will be readily apparent toone skilled in the art to which this invention pertains from a perusalof the claims and the following detailed description of preferredembodiments when read in conjunction with the appended drawings.

THE DRAWINGS

FIG. 1 is a pictorial representation of a cross section of a human earshowing pertinent anatomical features.

FIG. 2 is a pictorial representation of an embodiment of the earmold ofthe present invention inserted in the human ear (shown in crosssection).

FIG. 3 is a pictorial representation of the human ear showing abehind-the-ear hearing aid fitted to the earmold of the embodiment ofthe present invention shown in FIG. 2.

FIG. 4 is a pictorial representation of the acoustic conduction tube ofthe embodiment of the present invention shown in FIG. 2.

FIG. 5A is a partial pictorial representation of the flanged tip of theembodiment of the present invention shown in FIG. 2.

FIGS. 5B-5F are partial pictorial representations of alternativeembodiments of the flanged tip of the present invention.

FIG. 6 is a pictorial representation of an embodiment of the earmold ofthe present invention showing a concentric external tube.

FIG. 7 is a vertical cross section at mid-length of the embodiment ofFIG. 6.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to the figures where like elements have been given likenumerical designations to facilitate an understanding of the presentinvention, and particularly with reference to the embodiment of theearmold of the present invention illustrated in FIG. 2, the earmold maybe constructed of an acoustic conduction tube 60, a flanged tip 70, anda concha fitting 80. The resonant cavity 35 is formed between the tip 70and the tympanic membrane 30.

As seen in FIG. 3, the earmold of the present invention is fitted to ahearing aid 90, which may be located in any suitable position, such asbehind the ear, in the ear canal (not shown) or in the concha of the ear(not shown). The hearing aid 90 includes a microphone 91 to receiveunamplified sound and convert it to electronic impulses, an amplifier 92to amplify the received sound, a receiver 94 for converting electronicimpulses into sound waves, and a conduction hook 96, which may includean extension 97, to convey the amplified sound to the concha fitting 80.To assure proper operation of the present invention, the hearing aidshould neither prevent unamplified sound received at the ear fromentering the ear canal, nor should it contact a substantial portion ofthe skin lining the ear canal.

With further reference to FIGS. 2 and 3, one end of the concha fitting80 is attached to the end of the acoustic conduction tube 60 nearest theaperture 20, holding the tube in place so that it does not contactsubstantially the skin lining the ear canal. The fitting 80 is hollowand may be constructed of a suitable flexible material such as plastic.It may be a tube that fits into the concha 50 of the wearer and is heldin place with slight pressure on the walls of the concha. The other endof the fitting 80 is connected to the hearing aid. In operation,amplified sound from the hearing aid is conveyed by air conductionthrough the conduction hook 96 and extension 97 to the fitting 80 andinto the acoustic conduction tube 60. The length of the fitting 80 maybe adjusted as required to fit other hearing aid locations. When thehearing aid 90 fits into the concha or into the canal, the fitting 80may not be required.

With reference now to FIG. 4, the acoustic conduction tube 60 is hollowwith openings at the distal ends 62 and 64. The first end 62 is locatedinside the ear canal 10, preferably between the isthmus 40 and thetympanic membrane 30. While optimal results may be achieved when thefirst end 62 is located approximately 5 to 10 millimeters from thetympanic membrane 30, end 62 may be positioned in the canal as little as5 millimeters from the aperture 20. The second end 64 is adjacent theaperture 20. The location of this end may vary, depending on the type ofhearing aid and anatomy of the ear of the wearer. The tube 60 and thefitting 80 may be a single piece. The internal diameter of the tube 60is dependent on the amount of hearing loss and curvature of the canal.The external diameter of the tube 60 is smaller than the ear canal 10 toprevent substantial contact. An external diameter about one-half thediameter of the canal has been found suitable.

The tube 60 may be constructed of a material that is rigid or semi-rigidlongitudinally (that is, from end 62 to end 64) so that the tube may beinserted into the ear canal of the wearer and retain its shape. The tubeshould not sag or deform to touch the ear canal. To this end, it may beconstructed of acrylic plastic, polyvinyl chloride (PVC), silicone, orsimilar noncorrosive material suitable for use in a human body cavity.

With reference now to FIG. 5A, the flanged tip 70 may be affixed to thetube 60 at the end 62 to form the resonant cavity 35. The tip 70 isdesirably placed in the canal 10 so that between about one-third andabout eighty percent of the volume of the canal 10 is not substantiallyoccluded (i.e., reached by unamplified sound). The radially outward edge72 of the tip 70 conforms to the oval shape of the ear canal 10 adjacentthe end 62. The edge 72 creates a light seal by exerting only negligiblepressure on the canal 10 wall. The tip 70 has a hole 74 near its centercorresponding to the hole at the end 62 of the tube. The tip 70 may havea concavity facing the tympanic membrane 30 with tip thicknessdiminishing in the radially outward direction. The tip 70 should havesufficient thickness to give it lateral strength to resist movement ofthe end 62 to the wall of the canal 10. It has been found that suitableedge 72 thickness is approximately 0.05 to 2 millimeters. Thelongitudinal depth of the tip 70 (dimension " A") may be approximately 2to 8 millimeters.

The tip 70 is constructed of a flexible material suitable for use in ahuman body cavity, such as silicone, polyvinyl, soft acrylic, and thelike. While it has been found that these materials are suitable forreducing acoustic feedback through the ear canal, better results areachieved when the material is a syntactic foam (i.e., a composite of apolymeric matrix and microspheres). A suitable syntactic foam iscommercially available from Epic, Inc. of Hardy, Va., under thetrademark E-Compound and is more completely described in U.S. Pat. No.4,811,402, issued Mar. 7, 1989.

With reference now to FIGS. 5B-5F, wherein alternative embodiments ofthe flanged tip 70 are shown, the shape and location of the tip may bevaried to tune the cavity 35 to the needs of the wearer, or for usercomfort. As shown in FIG. 5B, the tip 70 may be arrayedcircumferentially about the tube 60, rather than at the end 62. As shownin FIG. 5C, the tip 70 may be cup shaped with the diameter of the edge72 smaller than the diameter of the canal. The depth of the cup(dimension "B" of this embodiment) may approximate the diameter of thecanal 10. The flanged tip 70 may also be flat, convex, or ellipsoidal(FIGS. 5D-5F, respectively).

The flexibility of the flanged tip serves several purposes. First, thetip serves to form a sealed cavity adjacent the tympanic membrane. Thesealing function reduces the amount of amplified sound which can traveloutwardly and feedback into the microphone of the hearing aid. Second,the flexibility permits the seal to be obtained with only slightpressure against the wall of the ear canal. Third, the flexibility ofthe flanged tip permits the tip to be oscillated by the natural,unamplified sounds which arrive by air conduction through the ear canal.Thus, the resonant cavity which is formed by the flanged tip has one ofits walls (the flanged tip) oscillating in response to the naturalsound. Such oscillation is believed to raise the resonant frequencies ofthe cavity so that more amplification can be utilized without discomfortto the user.

The phase relationship between the sounds which reach the sealed cavitynaturally through the ear canal and amplified through the conductiontube are complex and not totally understood in their effects on thesealed cavity. However, through conventional electronics, the phase ofthe amplified sound reaching the sealed cavity can be controlled withrespect to the phase of the natural sounds which oscillate the flangedtip. By varying the phase relationship between the two sounds, a user ofthe earmold of the present invention may find a phase relationship thatproduces the most natural and effective hearing.

One or more small vent holes 76 may be provided in the flanged tip forventing the sealed cavity to the open portion of the ear canal. Thevolume of the hole (as measured by its diameter and length) determinesthe amount of acoustic feedback introduced when vent holes are added.Vent holes in prior art earmolds have volumes large enough to allowacoustic feedback of high frequencies (greater than about 2700 Hz),typically because of the great length of the vent. In the presentinvention, however, the vent holes may be positioned on the tip so thattheir length is less than about two millimeters and preferably less than0.7 millimeters. The diameter of the vent may be about 0.5 millimeters.This small volume impedes passage of the high frequencies that may causeacoustic feedback. The cavity formed by the flanged tip is still to beconsidered sealed, regardless of the presence of the vent holes. Theterm "vent holes" as used herein also includes gaps in the radiallyoutward edge of the flanged tip so that the seal with the wall of theear canal is not complete.

With reference to new FIGS. 6 and 7, another embodiment of the presentinvention may include a second hollow tube external to and generallycoaxial with the acoustic conduction tube 60. The exterior of the secondtube 82 may contact the wall of the ear canal along a portion of thelength of the acoustic conduction tube 60. The second tube 82 maysupport conduction tube 60 with support members 90. This support may beneeded when, for example, the conduction tube 60 is not sufficientlyrigid to support its own weight.

The space between the two tubes 60 and 82 forms a sound conductionpassageway 85. The passageway 85 should be open at one end to theaperture 20 to receive unamplified sound and open at the other end tothe wall of the ear canal adjacent the top 70, preferably past theisthmus, to allow bone-conducted sounds to reach the ear canal. As inthe previously described embodiments the occlusion effect is preventedby venting bone-conducted low frequency sounds out of the ear canal,through passageway 85 in this embodiment. To this end, the supportmembers 90 should not block the passageway 85.

Preferably, the earmold of the present invention is custom manufacturedfor a particular wearer so that the appropriate tip seal is achieved.While it may be produced in various standard sizes or as aone-size-fits-all earmold, these types of off-the-shelf earmoldsprobably will not produce all of the performance and comfortimprovements found in the custom-made version.

The acoustic conduction tube 60 and flanged tip 70 may be constructedfrom a mold of the ear canal of the user. The mold is made by insertinga material such as silicone or ethyl methacrylate compound into the earto create a shape that replicates the diameter and bends of the canal.To prevent damage to the tympanic membrane, a cotton or foam block on athread is first inserted into the portion of the canal nearest themembrane. After allowing for shrinkage, the shape is used to form afemale mold of the canal. The flanged tip is formed by using the portionof the female mold that replicates the shape of the canal between theisthmus and the tympanic membrane (except the innermost unmoldedportion). The remainder of the female mold is used to form the tube. Thetube and the tip are joined by heating or with an adhesive. The acousticconduction path through the tube and tip is formed by drilling. Theexternal diameter of the tube portion is reduced by grinding to aboutone-half the diameter of the canal.

While preferred embodiments of the present invention have beendescribed, it is to be understood that the embodiments described areillustrative only and that the scope of the invention is to be definedsolely by the appended claims when accorded a full range of equivalence,many variations and modifications naturally occurring to those skilledin the art from a perusal hereof.

We claim:
 1. An earmold comprising:(a) an acoustic conduction tube openat both ends for conveying amplified sound to the tympanic membrane atthe inner end and the ear canal, said tube, when inserted into the earcanal, allowing unamplified sound received at the ear to reach into theear canal to a first position at least as deep as the osseous portionthereof; and (b) a flexible disk affixed to said tube so that when saidtube is inserted into the ear canal, said disk is adjacent said firstposition, said disk generally conforming to the ear canal at said firstposition, and having a hole coincident with the opening in the tube. 2.The earmold as defined in claim 1 wherein said first position isapproximately five to ten millimeters from the tympanic membrane.
 3. Theearmold as defined in claim 1 wherein said first position is between theisthmus of the ear canal and the tympanic membrane.
 4. The earmold asdefined in claim 1 wherein said tube comprises a longitudinally rigidtube having an outer diameter smaller than the ear canal.
 5. The earmoldas defined in claim 1 further comprising a second tube external to andgenerally coaxial with said acoustic conduction tube for forming a soundconduction passageway therebetween, said second tube when inserted intothe ear canal, generally conforming to the wall of the ear canal for aportion of the length of said acoustic conduction tube and havingsupport members for holding said acoustic conduction tube withoutblocking said passageway, said passageway being open at one distal endto the unamplified sound and at the other distal end to the wall of theear canal adjacent said first position.
 6. The earmold as defined inclaim 1 wherein said disk comprises a composite of polymeric matrix andmicrospheres.
 7. The earmold as defined in claim 1 wherein said diskcomprises a cup exerting nearly negligible pressure on the wall of theear canal.
 8. The earmold as defined in claim 1 wherein said disk has aconcavity facing the tympanic membrane and is less than 2 millimetersthick at the radially outward edge.
 9. The earmold as defined in claim 1wherein said disk has one or more vent holes.
 10. An earmold comprisingan acoustic conduction tube adopted for insertion into the ear canalwithout shielding the ear canal from unamplified sound, and a disk forcreating a resonant cavity next to the tympanic membrane affixed to saidtube, said disk adapted to contact the wall of the canal only in thearea of the canal between the isthmus and the tympanic membrane.
 11. Ahearing aid comprising:(a) amplifier means for receiving an amplifyingunamplified sound; (b) a tube adapted for conveying amplified soundsfrom said amplifier means to a first end of said tube inside the earcanal at least as deep as the osseous portion thereof; and (c) aflexible flanged tip affixed to said tube for positioning said tube in acanal, the radially outward edge of said flanged tip adapted forcontacting the wall of the canal adjacent said first end and for forminga resonant cavity next to the tympanic membrane, said tube and saidamplifier means, when inserted in the ear canal, leaving the portion ofthe canal extending from the ear aperture to said flanged tip exposed tothe unamplified sound.
 12. The hearing aid as defined in claim 11wherein said flanged tip comprises a cup affixed to said first end, theouter perimeter of said cup exerting nearly negligible pressure on saidwall.
 13. A method for making an earmold comprising the steps of:(a)forming an open-ended hollow tube having an external circumferentialsurface corresponding to the shape of the ear canal of the user, saidtube having a first distal end adapted to be positioned at least fivemillimeters inside the ear canal and a second distal end nearer the earaperture; (b) reducing the external diameter of said tube; and (c)affixing to said tube in the vicinity of said first end a disk offlexible material having a radially outward edge that generally conformsto the ear canal in the area of said first end.
 14. The method asdefined in claim 13 further comprising the steps of:(d) creating aconcavity on the face of said disk facing the tympanic membrane; and (e)reducing the thickness of the disk at the radially outward edge to lessthan 2 millimeters.
 15. The method as defined in claim 13 furthercomprising the step of:(d) creating one or more vent holes in said disk,said holes having a diameter of approximately 0.5 millimeters and alength of less than approximately two millimeters.
 16. The method asdefined in claim 13 further comprising the step of:(d) forming saidflexible material from a composite of polymeric matrix and microspheres.17. The method as defined in claim 13 wherein said first distal end isadapted to extend into the canal to a position between the isthmus andthe tympanic membrane and said tube is formed from a longitudinallyrigid material.
 18. A method for making a hearing aid comprising thesteps of:(a) providing amplifier means for receiving and amplifyingunamplified sound and for conveying the amplified sound to the earcanal, said amplifier means not preventing unamplified sound fromentering the ear canal when worn by a user; (b) forming an open-endedhollow acoustic conduction tube having an external diametercorresponding to the diameter of the ear canal and a first distal endadapted to be positioned at least five millimeters inside the ear canal;(c) reducing the external diameter of said tube whereby said tube doesnot contact the wall of the canal when inserted into the canal; (d)affixing a flexible flanged tip to said first end, said flanged tiphaving a radially outward edge generally conforming to the wall of theear canal when inserted into the ear canal; (e) forming a concavity onthe face of said flanged tip facing the tympanic membrane; (f) reducingthe thickness of said flange to less than about 2 millimeters at theradially outward edge; and (g) affixing the second distal end of saidtube to said amplifier means.
 19. A hearing aid comprising a disk forcreating a resonant cavity in an ear canal beyond the isthmus thereofnext to the tympanic membrane, and an amplifier for conveying amplifiedsound into said cavity and for allowing unamplified sound to reach intothe ear canal at least as far as the osseous portion thereof.
 20. Thehearing aid of claim 19 wherein said amplifier is located in the earcanal.
 21. The hearing aid of claim 19 wherein said resonant cavity iscreated beyond the narrowest portion of the isthmus.
 22. A method ofaiding hearing comprising the steps of:(a) flexibly sealing the earcanal to create a sealed cavity beyond the isthmus of the ear canal nextto the tympanic membrane; (b) providing an amplifier for conveyingamplified sound into said cavity; and (c) positioning said amplifier inthe ear canal so that unamplified sound can reach into the ear canal atleast as far as the osseous portion thereof.
 23. In a hearing aidcomprising sealing means for creating a cavity in an ear canal andamplifying means for conveying amplified sound into said cavity, theimprovement comprising placement of said sealing means and saidamplifying means so that unamplified sound reaches into the ear canal atleast as far as the osseous portion thereof.
 24. The hearing aid ofclaim 23 wherein said sealing means and said amplifying means are placedso that unamplified sound reaches into the ear canal at least as far asthe isthmus thereof.
 25. The hearing aid of claim 23 wherein saidsealing means is integral with said amplifying means.
 26. The earmold asdefined in claim 10 wherein said disk is adapted to contact the wall ofthe ear canal between the narrowest portion of the isthmus and thetympanic membrane.
 27. The earmold as defined in claim 3 wherein saidfirst position is between the narrowest portion of the isthmus and thetympanic membrane.
 28. The hearing aid of claim 23 wherein between aboutone-third and about eight percent of the volume of the ear canal is notsubstantially occluded by the hearing aid.